Capillary and venous blood glucose concentrations measured during intravenous insulin and glucose infusion: a comparison of steady and dynamic states.

Background: Patients undergoing intensive insulin therapy may have blood glucose (BG) samples drawn from arterial, capillary, or venous sources. This study compared capillary and venous BG across a range of glucose concentrations and under conditions of rapid change in BG. Methods: Following a 10-h fast, 40 adult patients with type 1 or 2 diabetes were connected to an automated glucose clamp device (Biostator (R), Miles Laboratories, Inc., Elkhart, IN) that induced a series of BG plateaus (hypoglycemic, euglycemic, hyperglycemic) and dynamic-state transitions (increasing, decreasing). Venous and capillary BG measurements were performed at different test points. Venous readings were adjusted to compensate for small time delays in obtaining the two samples. Results: Adjusted venous and capillary BG measurements were strongly correlated (R=0.84; P < 0.0001). The bias between BG sources showed a weak but significant correlation with rate of BG change in the hypoglycemic range (P = 0.0282) but not in euglycemic or hyperglycemic BG ranges. The bias observed during dynamic conditions was two to three times larger than that observed during steady states. During rapid increases and decreases in BG (>2mg/dL/min), 91.1% and 84.1% of paired capillary and venous results (n = 125), respectively, fell into Zone A of the consensus error grid versus 97.5% at slower rates. Conclusions: Capillary and venous BG values are similar under steady-state conditions but may differ under dynamic conditions. Variability associated with these differences was substantial during all states. As hospital insulin infusion protocols are widely implemented, healthcare providers need to be aware that glucose values may differ when blood is sampled from capillary and venous sites. Based on the tight ranges used in these protocols, these differences may impact insulin dosing decisions.